White-light emission derived from yttrium tungstate-chloride xerogel without activator ions

White xerogel powder of yttrium tungstate-chloride was synthesized, and its photoluminescence properties were investigated. Under the excitation of 254 nm, the xerogel phosphor exhibits emission ranging from 300 to 650 nm. This luminescent spectrum is identified as two emission bands of 300-400 and 400-650 nm due to different emission mechanism. While the emission band of 300-400 nm is ascribed to the charge transfer (CT) from O to metal W, the emission of 400-650 nm is attributed to electron-hole (e−-h+) carrier emission related to oxygen vacancies. By calcining the sample in reducing atmosphere, the number of oxygen vacancies acting as luminescence centers is increased. As a result, the emission intensity of 400-650 nm is significantly enhanced. Based on electron paramagnetic resonance and spectral analysis, the mechanism of peroxy-radical hole traps (PRHT) is proposed for the luminescence of 400-650 nm.